Pagination (page/2/) displaying 404 on archive pages for page Navi plugin

//Product Cat Pagination 
function modify_product_cat_query( $query ) {
	if (!is_admin() && $query->is_tax("product_cat")){
		 $query->set('posts_per_page', 8);
	}
}
add_action( 'pre_get_posts', 'modify_product_cat_query' );